Costa began the season in prolific fashion, scoring nine goals in seven matches, but he has missed Chelsea's last three fixtures because of a persistent hamstring injury.

The former Atletico Madrid man had also been suffering from a cold in the build-up to Sunday's match against Manchester United, but Mourinho revealed it was injury, rather than illness that ruled the £32million signing out of the match at Old Trafford.

The striker has been troubled by the hamstring problem for some time, but Mourinho believes it was exacerbated by Spain coach Del Bosque, who fielded the 26-year-old for back-to-back games against Slovakia and Luxembourg at the start of October.

"The virus is fine," the Chelsea manager said.

"It was hard, he had to go to the hospital and obviously it doesn't help him to recover from his injury. But he didn't play on Sunday because of the injury, not because of the virus.

"Diego has the hamstring (problem) because he played two matches in three days when he was not with us."